In the generation of electrical energy by burning coal to produce steam for the generators, a certain amount of waste material in the form of dust and dirt particles, fly ash, etc., is produced during combustion. Heretofore, these waste products were discharged through the smokestacks of the power plants and into the surrounding atmosphere. However, Environmental Protection Agency regulations now require that a large amount of such waste particles be collected before the fumes of combustion are discharged into the atmosphere. One type of apparatus for collecting such particles before they leave the stacks is an electrostatic precipitator (ESP).
These precipitators have been constructed in various forms and configurations. One of the usual types of precipitators consists of a plurality of collector electrode plates and corona electrode wires. The collector plates consist of a series of joined metal plates which are suspended from an upper support and located at a predetermined horizontal spaced relationship with respect to each other. A plurality of the electrode wires are located between the spaced plates and extend vertically therealong. These corona electrode wires, in combination with the collector electrode plates, impart a charge on the dust particles as they move through the spaces between the plates. The particles are charged at a different polarity than the electrode plate, whereby the dust particles are attracted to and collected on the electrode plates for subsequent removal from the bottom of the precipitator. The electrode plates are mounted on an upper supporting structure and are joined by a variety of construction methods.
One form of plate construction consists of a plurality of individual plates or panels, the edges of which are bent into flanges which are interlocked with the adjacent flange of the adjacent panel. These interlocking flanges form outwardly projecting ribs which extend vertically along the length of the collector plates. In addition to joining the individual electrode plates, the ribs provide strength to the assembled plates enabling the plates to maintain a flat parallel relationship with respect to the horizontally spaced adjacent plate.
It is critical that the plates maintain a constant predetermined horizontal spacing from each other, and in particular a constant spacing from the corona electrode wires extending between the spaced plates. This spacing is critical due to the high voltage which is applied to the plates and wires to prevent arcing therebetween and the subsequent destruction of the electrostatic field produced for collecting of the dust particles.
It is desirable that as high a voltage as possible be impressed on the plates and wires to more efficiently collect the particles passing between the plates. However, if this spacing is not maintained, the voltage must be reduced to prevent arcing, thereby reducing the efficiency of the precipitator.
Precipitators having the particular plate connection and supporting arrangements described above, as well as other plate arrangements, sometime experience a serious problem of plate warping. Plate warping can occur during the life of the precipitator for various known and unknown reasons and seriously affects the spacing between the plates and electrode wire. This warping increases the danger of arcing between the wire and adjacent plate requiring the lowering of the applied voltage and consequently lowering of the efficiency of the precipitator.
In order to maintain the plates in vertical alignment to eliminate or reduce plate warpage, various methods and spacers have been developed. One method involves placing kinks in the warped plate ribs. This solves the problem but only for short periods of time. The most satisfactory means is the use of various spacer bars or cross braces which are attached to the plate, usually by welding. These braces extend horizontally between the plates and provide sufficient strength and rigidity to maintain the plates in their spaced parallel relationship. However, the installation of such spacer bars is extremely expensive and time consuming. A workman must enter between the spaced plates to mechanically attach the spacer to the plates. This attachment can only be done after much of the supporting hardware for the plates and corona wires are removed. This increases considerably the "downtime" of the precipitator as well as increased labor cost. Various types of plate straighteners or cross braces are shown in U.S. Pat. Nos. 2,822,057; 3,018,844; 3,028,715; 3,114,616; 3,418,792; 3,678,653; 3,836,135; 4,007,023; 4,239,514; and 4,240,810.
Although many of plate spacers of these patents perform satisfactory, they are expensive to install since it requires partial dismantling of the electrode plates and wire supporting system so that a workman can enter the spaces between the plates for installing the same. Likewise, many of these plate straighteners are intended for new installation only and are not practical for installation in existing precipitators should the plate warpage occur after the precipitator has been in service for some time.
Accordingly, the need has existed for an improved plate spacer for electrostatic precipitators which can be installed at various vertical positions along the length of the collector electrode plates without requiring dismantling of the supports of the collector electrodes or corona electrode wires and which is relatively inexpensive, yet highly effective in maintaining the plates in a predetermined spaced relationship.